Some Mesoscopic Rings: Exact Simulations and Experiment

G. Kamieniarza, R. Matysiakb, A. Caramico D'Auriac, F. Espositoc and C. Benellid aComputational Physics Division, Institute of Physics, A. Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland bInstitute of Technology, Pedagogical University in Zielona Góra, Poland cDipartimento di Scienze Fisiche, Università di Napoli "Federico II", Piazzale Tecchio, 80125 Napoli and INFM Unità di Napoli, Italy dDipartimento di Chimica, Università di Firenze' via Maragliano 77, 50144 Firenze, Italy

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Received: July 3, 2000; revised version September 25, 2000

A numerical transfer-matrix approach and an exact diagonalization technique exploiting the point-group symmetry are worked out in the framework of quantum statistical mechanics and group theory for finite rings. They are applied to spin models of the high nuclearity cyclic clusters [Mn(hfac)2NITPh]6 and Ni12(O2CMe)12(chp)12(H2O)6(THF)6. The microscopic parameters of both molecules (J/kB=350±10 K and J/kB=8.5 K±0.5, g=2.23±0.01, respectively) are then obtained from a fit of the theoretical susceptibility curves to the experimental results which are supplemented for Ni12 by new low-temperature measurements.

DOI: 10.12693/APhysPolA.98.721 PACS numbers: 75.10.Jm, 75.40.Cx, 75.40.Mg